Three dimensional (3D) imaging methods based on the above principles are described in detail in the documents no. WO 94/23541 and WO98/34411, the contents of which is presumed to be known for understanding the present invention. 3D images contain more information than 2D images. To display a 3D image, an appropriate number of screen points (spots) must be generated, and, in the case of a moving image, taking into consideration the change of the frames, an appropriate spot/sec ratio must be generated as well. The number of screen points (spots) is basically the product of the image resolution and the angle resolution (that is, the number of distinguishable views or viewing zones). In addition, in the case of a moving image, the number of screen points required within one single frame must be multiplied by the number of frames changed in one second (frame/sec), thus giving the number of screen points to be generated every second.
The basic problem is how to generate the required number of imaging screen points (spots) within a given unit of time (spot/sec):
One possible solution is to perform the multiplication with the time; in which case faster devices are needed, as it is described in U.S. Pat. No. 6,157,424. Such a device is not yet available in practice, or is only able to display a limited number of views. These devices apply fast LCD screens or other fast light valves, placed in two or three subsequent planes.
The second solution is spatial division, that is, the required number of screen points are generated paralelly and appropriately organised. In practice, displays of normal speed must be used, but with a greater number of pixels (high resolution), or more displays with normal resolution. The disadvantage of this approach is that it requires more space. Such are lenticular systems, where different directions are created at the expense of resolution; for example, to create ten directions a device with a 10-fold resolution is needed, where every tenth screen point is associated to a certain direction, or, alternatively, a screen (display) is divided into ten parts. Different versions of these solutions are now known.
The third possibility is to combine the two methods, making optimal use of the speed and resolution of the devices, taking into consideration the technological features and limitations of the screen point generating element; for example, for generating 30 views, ten pieces of triple-speed devices or with a ten-fold resolution are applied. The spatially separated the 10-fold number of screen points is divided in time by 3 different light sources—typically from different directions.
The present invention describes a method and apparatus, which meet the above requirements, with a method that can be realised with real, existing technologies, based on the second and third solutions.
The purpose of the present invention is to provide an improved method and apparatus which can produce high quality colour images with adequately high frame frequency, that is, which makes it possible to produce moving 3D colour images, as well. To solve this task, the invention basically requires a new optical arrangement.
An important element of the known 3D imaging systems described above is a relatively small light source emitting light beams of varying intensity (and preferably of different colours) in different directions. In document no. WO 98/3441 this is created through an acousto-optical deflector which deflects and modulates a laser beam as a function of time. Thus light beams are generated and emitted in different directions, and these light beams are differently modulated in different directions.